Question

A frictionless piston–cylinder device contains 2.5 kg of nitrogen at 100 kPa and 250 K. Nitrogen is now compressed slowly according to the relation PV1.4 = constant until it reaches a final temperature of 450 K. Calculate the work input during this process. The gas constant for nitrogen is R = 0.2968 kJ/kg·K.

Answer 1

Answer: -371kJ

Explanation:

Answer 2

Answer:

The work input during this process is 371 kJ.

Explanation:

For a polytropic process, as this one, work can be computed from the formula

$W=\frac{mR\left(T_2-T_1\right)}{1-n}=\frac{2.5kg \times 0.2968\frac{kJ}{kg\times K}\left(450K-250K\right)}{1-1.4}=-371kJ$

Notice that the answer units are kJ and it's negative because the work is done ON the system.